Influence of testosterone on sexual behaviour in women

A variety of models have been used to test the relationship between testosterone and sexuality in women. Because plasma testosterone levels peak around the time of ovulation (Ferin 1996), one investigational strategy involved monitoring changes in several aspects of sexual behaviour at differerent points during the menstrual cycle. As plasma levels of estradiol also reach their highest point at the ovula-tory phase, this research design makes it difficult to prove that testosterone alone induces the increase in sexual behaviour during the midcycle portion of the menstrual cycle observed in some studies (Adams etal. 1978; Harvey 1987; Dennerstein et al. 1994; Matteo and Rissman 1984). But several well-controlled correlational studies measuring circulating testosterone in women found evidence of an androgenic enhancement of sexual behaviour. Higher testosterone levels (midcycle peaks or average levels of plasma testosterone throughout the cycle) were associated with less sexual avoidance (Persky et al. 1982); more sexual gratification (Persky et al. 1978; 1982),sexual thoughts (Alexander and Sherwin 1993),and initiation of sexual activity (Morris et al. 1987); higher levels of sexual interest and desire (Alexander and Sherwin 1993; Alexander et al. 1990; Leiblum et al. 1983) and vasoconges-tive responses to erotic films (Schreiner-Engel et al. 1981); increased frequency of masturbation (Bancroft et al. 1983) and coitus (Morris et al. 1987); and a higher number of sexual partners (Cashdan 1995).

The positive relationship between testosterone and various measures of sexual interest and behaviour is intriguing; on the other hand, most studies failed to provide evidence of a peak of sexual behaviour at the time of the midcycle peak in testosterone. However, this is no argument against any testosterone-sexuality relationship in females, as an increase in testosterone does not have to produce an immediate behavioural response. For instance, the latency between androgen administration and increases in sexual desire in hypogonadal men ranges from days to several weeks.

The most powerful design for the study of the specificity of testosterone influence involves hormone replacement therapy in women who are oophorectomized. It is common clinical practise to treat these patients with estrogen replacement, but substitution of testosterone is also sensible as the women are deprived of ovarian androgen production as well. Several studies on naturally or surgically menopausal women have shown - without contradictory evidence - that administration of testosterone, either alone or in addition to an estrogen replacement regimen, is more effective than estrogens alone or a placebo. In particular, an increase in sexual desire and phantasies was elicited, but also in sexual arousal, sexual sensation, and in coital or orgasmic frequency, and masturbation frequency (Davis and Tan 2001; Sarrel et al. 1998; Sherwin, 2002; Sherwin and Gelfand 1987; Sherwin et al. 1985; Shifren etal. 2000).

Although there is converging evidence from these correlational and experimental investigations that testosterone enhances male and female sexual behaviour, such as sexual desire or sexual phantasies, the underlying behavioural mechanism is not fully understood. Testosterone might have direct effects on cognitive behaviour, e.g., influence the awareness of sexual cues (Alexander and Sherwin 1993), or may act peripherally to enhance sexual pleasure and, thereby increase sexual desire (Davidson etal. 1982). Myers and Morokoff (1986) could show that serum testosterone levels in women correlated with genital responses and subjective physical sensation (i.e., vaginal lubrication and breast sensation) in response to erotic visual stimulation.

Whether the effects of androgen were mediated by direct action on the nervous system, by an effect on the genital organs, or both had not been investigated in their study. At present, only data obtained from investigations of ovarectomized animals are available. Traish et al. (2002) characterized androgen receptor expression in rabbit vaginal tissues from control and ovariectomized animals treated with or without androgen replacement therapy. They found that vaginal tissues express androgen receptors and that the expression of these receptors is regulateddifferently in the proximal and distal vagina by androgens and estrogens. They concluded that androgens appear to play a role in vaginal and clitoral function during genital sexual arousal.

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